Gambling warning labels: Differing effects of message length and message format

“Return-to-player” warning labels are used to display the long-run cost of gambling on electronic gambling machines in several jurisdictions. For example, a return-to-player of 90% means that for every $100 bet on average $90 is paid out in prizes. Some previous research suggests that gamblers perceive a lower chance of winning and have a better objective understanding when return-to-player information is instead restated in the “house-edge” format, e.g., “This game keeps 10% of all money bet on average.” Here we test another potential risk communication improvement: making return-to-player messages longer, by clarifying that the information applies only in the statistical long-run. It was suggested that gamblers might understand this message better than the return-to-player at the conclusion of a court case brought against an Australian casino. In this study, Australian participants (N = 603) were presented with either a standard return-to-player message, a longer “return-to-players” message, or a house-edge message. The longer return-to-players message was understood correctly more frequently than the return-to-player message, but the house-edge message was understood best of all. Participants perceived the lowest chance of winning with the longer return-to-players message. The house-edge format appears easiest for gamblers to correctly understand, but longer warning labels might be the best at warning gamblers about the long-run costs of gambling on electronic gambling machines.